Apparatus for identifying peak amplitudes of variable signals



R. F. KLAVER 3,412,330

S FOR IDENTIFYING PEAK AMPLITUDES OF VARIABLE SIGNALS Nov. 19, 1968APPARATU 3 Sheets-Sheet l Filed Jan. 9, 1967 w mm J MM EE P H R ill-"E TN R m s in MM U N a M IIIL III. I Y Z R lama v H EU I f H A D m mm m MMT v G s a R M IIYSUE u a 5 R I E C S Wm n 5 D s G M. W m w J A M N L EA A B .NM. Au ||||W||||| R F- a n w. W K A R M a n 5 PEAK HEIGHTS S R EB M U N S S A M FIG.1

PRINTED I PEAK HEIGHTS ANALOG SPECTRUM SIGNAL INPUT BIAS LEVEL NVENTOR F3 RUDOLF r. maven CONTENTS DA-REGISTER United States Patent "ice3,412,330 APPARATUS FOR IDENTIFYING PEAK AMPLI- TUDES 0F VARIABLESIGNALS Rudolf F. Klaver, 1440 Portland Ave., Albany, Calif. 94706Continuation-impart of application Ser. No. 256,064, Feb. 4, 1963. Thisapplication Jan. 9, 1967, Ser. No. 622,838

1 Claim. (Cl. 324-103) ABSTRACT OF THE DISCLOSURE An apparatus foridentifying the attainment of a peak along a signal having amplitudevariations with time. The amplitude of the time varying signal iscontinuously monitored and a measure of its amplitude is stored in ameasuring device. The instantaneous value of the signal is continuouslycompared to the stored signal plus and minus a fixed bias signal. Whenthe input signal is more than the stored signal plus the bias, a newmeasure for the stored signal is produced representing the value of theinput signal. When the stored signal plus the bias is more than theinput signal and a subsequent measure of the input signal minus the biasis less than the stored signal, a peak in the input signal isidentified. The identification of a peak causes the last stored quantityto be transmitted to a printer to be identified as a peak on the timevarying signal.

This application is a continuation-in-part of Ser. No. 256,064, filedFeb. 4, 1963, now abandoned.

This invention relates to a method and apparatus for identifyingamplitude peaks along a continuous signal having amplitude variationswith time. More particularly the invention relates to a method andapparatus for automatically generating signals representative ofidentified peak values along a first continuous time varying signal andconcurrently generating a signal representative of the value of a secondtime varying signal at the time of identification of a peak in saidfirst signal.

In the various arts where continuous signals representing difi'erentscientific phenomena are observed and studied, it is usually thespecific events and the values within the continuous signals that are ofimportance to the observer. Generally it is desired to provide apermanent record of these specific events or values for future referenceor for study. Quite often, interrelated values of two continuous signalsrepresent the significant scientific information that the observer seeksto determine. One example of an observation of continuous signalsrepresenting scientific information is found in the art of massspectrometry wherein qualitative and quantitative values representingvarious materials within a sample may be determined. In a massspectrometer, a gaseous sample under analysis is ionized and thensubjected to controlled electrostatic and/ or electromagnetic fields.The ionized gas is focused into a beam and then manipulated by thecontrolled fields. By varying one or both of the electrostatic orelectromagnetic fields, ion beams having a particular mass to chargeratio (M C can be focused to strike a collector appropriately positionedin the path of the ionized beams. The ions striking the collector causean electrical current to flow from the collector and that current willvary in accordance with the intensity of the beams striking thecollector. The magnitude of the electrical current flowing from thecollector fluctuates between peaks and valleys with the peak heightswithin the continuous signal representing the quantities of ions atvarious mass charge ratios. A coincident value of the variation in thecontrolled fields may be used to identify the mass of the particularions striking the collector and causing the electrical current. SelectedPatented Nov. 19, 1968 peaks along the continuous signal may then becorrelated with the value of the controlled fields at the instant of apeak to derive both a qualitative and a quantitative representation ofthe ion beam passing through the spectrometer. A continuously recordedand printed record of these peak heights and the values of relatedcontrolled fields furnishes one performing the mass spectrometeranalysis with both the qualitative and quantitative values of the sampleunder analysis.

Most of the present mass spectrometers provide output records in analogform, requiring detailed and timeconsuming interpretations of the valuesof the peak heights and their relationship to the mass-charge ratio.Some forms of apparatus are known which will automatically print outpeak heights and mass numbers from information derived from a massspectrometer, and some of these forms of apparatus will provide theinformation in digital form. However, many of these devices have beenfound to be unreliable or slow, some provide mere approximations of theactual relationship between signal peaks and time along the record, andsome require partial manual control in order to obtain records withinthe desired signal ranges supplied from the mass spectrometer.

An object of the present invention is a method and apparatus for theidentification of signal peaks within a continuous varying signal inaccordance with a novel logic program.

A further object of the present invention is to provide a simplifiedmethod and apparatus for automatically digitizing amplitude valueswithin two continuous signals and for printing representations oflegitimate peak signal variations in a first of the continuous signalsalong with the instantaneous value of a second of the continuous signalsrelated to the first signal.

Further objects and features of the invention will be readily apparentto those skilled in the art from the specification and appended drawingsillustrating a certain preferred embodiment in which:

FIG. 1 is a simplified block diagram of a function that can be performedby the method and apparatus of the present invention.

FIG. 2 is an expanded block diagram illustration of the circuits andtheir interconnections as employed in the present invention to performthe function illustrated in FIG. '1.

FIG. 3 is an illustration of the procedure followed by the apparatus ofFIG. 2 for identifying signal peaks along a varying amplitude analogsignal.

FIG. 4 is a block diagram illustration of an alternative form ofapparatus for performing the method of the pres ent invention.

The method and apparatus of the present invention are capable ofhandling input data from many different processes. As here illustratedand described the invention is related to a mass spectrometer. It shouldbe understood, however, that the invention is not restricted to theillustrated use.

In FIG. 1, the present invention is illustrated as part of the massspectrum digitizer generally enclosed within the dotted lines 10. Whilenot necessarily restricted to being energized in or from any particularsignal source, the digitizer is illustrated as being connected to a massspectrometer 11 having a first signal or analog spectrum signal outputat 12 and a second signal or analog mass number signal output at 13. Theanalog spectrum signal is supplied to a peak height digitizer 14 wherethe analog spectrum signals are digitized, or converted to digitalsignals, and where a peak along the analog signal is identified. Digitalpeak height signals are supplied at its output on conductor 15. The peakheight digitizer further supplies a print command on conductor 16Whenever a peak is identified in the analog signal. A further output 3is provided from the digitizer on conductor 17 identified as a holdsignal to maintain an associated piece of equipment in one fixedcondition until the peak height digitizer has provided a second commandsignal.

The analog mass number signals are supplied to a mass number digitizer18 where the analog input signals are converted to digital outputsignals on conductor 19. In the apparatus as illustrated in FIG. 1 thehold signal on conductor 17 from the peak height digitizer is suppliedto the mass number digitizer, simultaneously with the print commandsignal on conductor 16, to hold it in a fixed position until the valuethat its digitizer has attained has been transferred for recording.

The two digital signals from the digitizers 14 and 18 are supplied to aprinter 21 where the digital input signals are converted to visualsignals on parallel columns of a paper tape such as illustrated at 22.The printer is actuated to print a parallel column of digital numbers onreceiving a print command on conductor 16 from the digitizer 14. Itshould be understood that with commercially available equipment thesignals way also be recorded by other forms of digital recorders such ascards, paper tape or magnetic tape.

In the simplified form as illustrated in FIG. 1 the peak heightdigitizer of the present invention is capable of taking two inputsignals from one or more energizing devices and separately convertingthese signals to digital form for energization of a printing device soas to produce a visible output record of the variations within the twoinput analog signals. In the present invention a novel cooperation oflogic circuits is employed to identify the existence of a peak withinone of the analog signals so that the identification of a peak in thatsignal may be employed to actuate a printing device to cause separaterecords of each of the digitized quantities to be printed. The logiccircuits and their manner of interconnection are illustrated in FIG. 2where the elements of the mass spectrum digitizer are separated bydotted lines and identified, where applicable, by the same charactersappearing in FIG. 1.

The peak height digitizer 14 includes a summing junction at 23, acomparator 24, a logic circuit 25, a digital to analog converter anddigital storage device 26 with associated interconnecting and gatingcircuits, to be later described, for producing an output signal atconductor 15 to the printer 21. The mass number digitizer 18 isillustrated as including a ratiometer 27 for converting the input analogsignal to an output digital signal on conductor 19 for supply to theprinter 21. The hold signal conductor 17 interconnecting the twodigitizers 14 and 18 is illustrated as well as the print command signalconductor 16 for actuation of the printer 21.

The peak height digitizer 14 of FIGS. 1 and 2 is intended to perform thefunction illustrated in FIG. 3. In that figure an analog spectrum signalis illustrated as having several amplitude variations including peaksattained at 20 and 30 to be converted to digital form by a comparisonoperation in a series of steps along the signal. The digitizer mustfirst sort input noise or signals smaller than a preset level fromdesired signals. This function is performed by inserting a predeterminedoffset signal level. The digitizer then systematically follows signalvariations and repeatedly performs a digitization of the input signal asthe input exceeds previously stored digital quantities. False signalpeaks due to small noise signals, inherent in the input signal, areeliminated by requiring the input signal to exceed the stored signal bya bias quantity larger than the noise signals.

In the procedure illustrated in FIG. 3, at each point a, b, c, d, etc.,the contents of the digital to analog storage register are fixed and theanalog-input signal is continuously compared with the algebraic sum ofthe stored signal and a bias signal. The bias signal is repeatedlyalternated in polarity. As long as the analog signal differs less thanthe bias from the stored quantity no other action than continuouslyalternating the bias polarity is taken and the digital to analog storagedoes not change its contents, as for instance between points b and c. Ifthe input analog signal increases to point 0, however, this signalbecomes larger than the stored quantity b plus the bias and the digitalvoltmeter will make a complete new conversion ending with a storedquantity equal to the input signal at point c (assuming that the rate ofrise of the input signal is relatively low as compared with theconversion rate of the digital voltmeter).

The above described process will repeat itself until, as illustrated ata comparison identified as n-l, the analog signal becomes less than thestored digital signal minus the bias. When that condition has beenidentified, a print command signal is transmitted from the peak heightdigitizer and the printer 21 will be commanded to record digitalquantities. During the printing period the digitizer will be given ahold signal to prevent a digital change before the recording has beencompleted. It should be noted that a peak is detected and a printcommand supplied only when the logic circuit identifies an analog signalless than the last stored digital quantity minus the bias preceded by ananalog signal larger than the last stored digital quantity.

After the prescribed hold period has expired, the input analog signal isagain digitized and stored and then compared to the stored signal plusand minus bias during which time no print command pulses are generatedon line 16 until the input analog signal changes its direction of slopeand begins to exceed the last stored quantity plus the bias. Theapparatus of the present invention then again makes the comparisonbetween the analog signal and the stored signal with the bias signaluntil the next peak is identified in the same manner that the previouspeak was identified. With each sensed peak, a print command is suppliedfrom the converter and storage 26 to the printer 21 to again record thedigitized quantities.

The apparatus for the identification of a peak along an input analogsignal in the manner illustrated in FIG. 3 will now be described. Toinitiate operation of the digitizer, a start pulse should be supplied onconductor 28 through normally open pushbutton switch 29 to clear thesystem. In FIG. 2 an input analog signal is supplied at conductor 12.That signal is to be systematically moni- H tored so as to identify theoccurrence of a peak in its amplitude. As previously described, the peakis identified by comparing the input signal to stored quantitiesrepresenting previous signal amplitudes. After the start pulse theinitial stored signal is zero and that signal is repeatedly combinedwith a fixed bias quantity for comparison to the analog input signal.

The combination of the stored and bias signal is an algebraiccombination, alternately the positive bias signal and then the negativebias signal. The summation is accomplished in the summing junction 23.The alternately summed signals are supplied in sequence as an input tocomparator 24 while the input analog signal is continuously supplied asthe second input. In the comparator the two signals are compared and,when the previously described criteria have been satisfied, outputsignals are supplied to the logic circuit 25.

The signals supplied to the summing junction 23 are the signals onconductors 31 and 32 of FIG. 2 and constitute, respectively, thequantity from converter 26 and the signal from one of a pair of gates 33(normally open) or 34 (normally closed). For simplicity of description,it will be assumed that the input analog signal on conductor 12 haspositive peaks, that the signal from the digital to analog converter 26on conductor 31 is zero, having been reset, and further, that gate 34 isin its normally closed condition while gate 33 is normally open. In thatbeginning condition, the signal from an offset adjustor 35 will besupplied through gate 33 to conductor 32 and to the summing junction 23.The summing junction 23 performs a sequential algebraic summation of thetwo input signals and supplies an output to the comparator 24representative of that summation.

With the signal on conductor 31 set at zero and the signal on conductor32 at the offset value, in a negative polarity with respect to the inputsignal, there will be no positive output signal from the comparatoruntil the analog signal on conductor 12 exceeds the value of the oilsetsignal. So long as the input from the analog signal remains less thanthe oifset, the peak height digitizer is in a fixed condition performingonly a polarity testing function. When the input analog signal exceedsthe offset signal and a positive signal is fed to the comparator 24, thecomparator conditions the logic circuit 25 to supply a signal onconductor 36 to close the gate 33 and to supply a signal on conductor 37to command the digital to analog converter 26 to increase its value tothe value of the incoming analog signal. The converter continues toincrease its value at a high speed, typically in less than 0.5millisecond until the output from the summing junction 23 equal-s theinput signal. When the converter 26 has attained the commanded signal orquantity, it then stores that quantity until it is further commanded. Atthis time, the logic circuit 25 supplies a signal on conductor 38 tochange gate 34 from a normally closed to an open gate and thus to add apreadjusted bias from bias generator 39 through polarity control 41 andgate 34 to the summing junction 23 on conductor 32. The polarity control41 changes the polarity of the bias supplied from bias generator 39 fromplus to minus in accordance with a signal on conductor 42 supplied fromthe logic circuits 25. Reversal of polarity of the bias is accomplishedat a constantly repeating rate in accordance with signals from a timingdevice 43 herein illustrated as 60 kc. clock. The comparator 24therefore receives an input analog signal on conductor 12 and a signalfrom summing junction 23 constituting a stored signal from the converterand a bias signal varying between plus and minus at regular intervals inaccordance with the signals from the pulsing clock 43. So long as theinput signal remains within the limits of the stored value from theconverter 26 plus or minus the value of the bias, the only action thatthe comparator 24 and the logic circuit 25 perform is to cause the biasto be switched in polarity with every clock pulse.

When the input signal on conductor 12 increases to become larger thanthe stored value plus the bias signal, a new command from comparator 24is supplied to the logic circuits 25 and the logic circuit senses thissignal increase and supplies a signal along conductor 44 to reinitiate astart pulse to the logic circuit 25 on conductor 28. The pulse onconductor 28 causes the system to repeat the previously described logicstep and causes the digital to analog converter and storage to clear andthen assume a new value in accordance with the input analog signal. SolOng as the input analog signal is increasing, a series of commands willoccur along the conductors 44 and 28 from the logic circuit toreinitiate the logic function and to continue the repeated conversion ofthe analog signal to new digital quantities and the storage of the newquantity. It should be noted that each time the input signal exceeds thestored signal by the bias quantity, the logic circuit causes theconverter to make a new reading and to start all over again.

When a peak is attained as is illustrated .at 20 in FIG. 3 the logiccircuit 25 will eventually be confronted with an indication thattheinput analog signal on conductor 12 has become less than the signalsupplied on conductor 31 from the converter 26 minus the bias suppliedon conductor 32 from the bias generator 39. When that condition occursthe logic circuit 25 provides a pulse on conductors 45 and 46 to supplya print command through normally open gate 47 to print command conductor16. The printer 21 is then commanded to print the quantity within thestorage section of the digital to analog converter and. storage 26 as itappears on conductor 15. The printer 6 of course, will also print thequantity representing th mass number as supplied on conductor 19, themass number quantity being determined in a manner to be hereinafterdescribed. The print command is also supplied to a delay circuit 48 onconductor 49 from the print command conductor 16.

The delay circuit interrupts the operation of the peak height digitizingfunctions until the printer 21 has had suflicient time to complete itsprinting operation. The digitizing operation of the present invention isinitiated by pulses carried on conductor 28 and supplied whenever thelogic 25 has identified a particular condition. Actually the logic 25shuts itself off and then starts itself again with the pulse onconductor 28. The time delay 48 interrupts the immediate initiation ofthe operation by Withholding the start pulse, and in so doing preventsany changes in the stored digital quantity as the printing is beingaccomplished.

The print command supplied on conductor 45, through gate 47 and onconductor 49 also 'actuates a flip-flop circuit 51 to supply a signal onconductor 52 to change the conditions of gate 47 to close that gate andthus block another print command until the circuit has been reset. Theflip-flop circuit 51 further supplies a command on conductor 53 to agate 54 to open that gate so that any further commands appearing onconductor 45 will pass through gate 54 to the start command conductor28. Each time a pulse appears on conductor 28, the storage will becleared and a new digital conversion of the input analog signal will bemade and stor.-d. As further comparisons are made between the inputanalog signal, the stored signal in the converter 26 and the signal fromthe bias generator 39, the logic circuit 25 will continue to detect aninput analog signal that is less than the stored signal minus the bias,and subsequent repeat commands will be supplied to conductor 45 and bepassed through gate 54 to cause the logic circuit to continue itsrepeated conversions. No new print commands can be supplied however, inthat gate 47 is closed.

When the input analog signal changes its direction of slope and beginsto increase in a positive direction, it will be compared to the quantitythen stored in the converter 26 plus and minus the bias quantity frombias generator 39. When the input signal exceeds the stored signal plusthe bias, the logic circuit 25 will again supply a command alongconductor 44 to conductor 28 to the logic circuit. The command onconductor 44 will also appear on conductor 55 to return flip-flop 51 toits original condition and will cause gate 47 to be returned to anormally open condition and gate 54 to be changed to a normally closedcondition. The logic circuit will then continue its comparison betweenthe input analog signal and the stored quantity with the bias signaluntil it again recognizes the existence of a peak in the input signalwhereupon a signal will be supplied upon conductor 45 to again commandthe printer 21 to print a digital quantity. Each print command willcause the time delay 48 to become effective and will actuate flip-flop51. A device capable of performing the duty of the logic circuit 25 isillustrated in U.S. Patent 3,052,880, issued Sept. 4, 1962 to F. M.Young et al.

The mass number digitizer 18 is supplied with an analog signalrepresenting a usually continuously varying voltage. That varyingvoltage may represent a variation in the electromagnetic field or theelectrostatic field in the case of a mass spectrometer. The signal tcthe mass number digitizer may also be an analog signal from any otherquantity that will represent the mass numbers identifying the particularions striking the collector within the spectrometer. In the digitizer 18the input analog signal is compared to a voltage from source 56 that maybe adjustable to provide for the ranges of operation in the mass numberdigitizer. The analog sigal and the adjustable signal are supplied to aratiometer 27 where the ratio of these two signals is digitized andcontinuously supplied to the printer 21 on conductor 19. The ratiometerfunctions as a digitizing comparator to supply digital signals to theprinter when a print command appears on conductor 16 to actuate timedelay 48 and when a blocking or hold signal is supplied on conductor 17to the ratiometer 27. For the period of time delay 48 the ratiometerwill not supply new signals to the printer 21; however, after the timehas expired, the mass number signals will again be continuouslysupplied.

The input connections to the ratiometer, connected as shown in FIG. 2,will provide a digital output which is inversely proportional to the MSaccelerating voltage. This is desirable for mass spectrometers that scanthe spectrum by varying this voltage since then the digital ratiometeroutput is directly proportional to mass number.

The operation of the apparatus as illustrated in FIGS. 1 and 2 will nowbe described. With an input signal supplied along conductor 12 and asummation signal from summing junction 23, the comparator 24 supplies asignal to the logic circuit 25. The logic circuit will make a continuoussign test on the value of the input signal as compared to the signalfrom offset generator 35. If the sign test indicates a negativequantity, the logic circuit has then recognized that the input voltageis smaller than the offset and the logic circuit will remain in a signtest state. If, at some time, the input becomes larger than the offset,the result of the sign test will be positive and a pulse will appear onconductor 36 to convert gate 33 from normally open to normally closedand signals will appear on line 37 to command the digital to analogconverter to increase its stored value to that of the analog inputsignal. When this has been accomplished a pulse will appear on conductor38 to convert gate 34 from a normally closed to a normally opencondition. Thereafter pulses will appear on conductor 42 at intervalsdetermined by clock 43 to change repeatedly the polarity of the biasfrom bias generator 39 by the operation of polarity changer 41.

Thus after a positive quantity has been identified, the bias supplied onconductor 32 will be added to the signal appearing on conductor 31 andrepresenting quantity stored in the analog digital converter 26. The sumof the two signals will be compared to the input analog signal.Subsequently the polarity of the bias signal will be reversed and thecomparator will compare the input signal to the stored quantity minusthe bias. The logic circuit will then follow the following systematicdeterminations:

(1) With a sign test positive and the bias positive, the

logic circuit will command itself to make a new conversion and commandthe digital to analog converter and storage to assume the value nowpresent on input line 12.

(2) With a test positive and the bias negative, the logic circuit willkey the polarity controlling device 41 to reverse its polarity.

(3) With a sign test negative and the bias positive another signal willappear on conductor 42 to cause polarity controlling device 41 to changethe polarity of the bias signal.

(4) With a sign test negative and the bias negative the print commandwill appear on conductor 45 and Will be transmitted to conductor 16 tocause the printer 21 to print the quantity stored in the storage 26along with a quantity from the mass number digitizer appearing onconductor 19.

In cases 2 and 3 the difierence between the input signal and thesummation signal is less than the bias, and the peak height digitizercontinues to monitor this difference by continuously changing the biaspolarity every clock pulse. In case 1, the input signal has increased bymore than the bias and a complete new conversion is made. In case 4 thesignal has decreased by more than the bias and the quantity stored inthe analog to digital storage is as close to the actual peak height asis possible and is, therefore, displayed and printed out. The print-outcommand is carried to the delay circuit 48 to block changes in thesignal supplied to the printer for the period of the time delay.

If the first comparison after the time delay has expired occurs on thedown slope of an input signal and the signal continues to decrease,print commands would normally be generated in accordance with the logicdescribed in case 4. The operation of the flip-flop 51 by a printcommand appearing on conductors 16 and 49, however, closes the gate 47through conductor 52 and prevents further print commands from beingcarried to the printer until after a change in polarity of the inputsignal has been sensed. The change in operation of the logic circuitafter a print-out command is as follows:

(5) With a sign test positive and bias positive, a reset pulse issupplied to the flip-flop 51 on conductor 55 from conductor 44 and thelogic circuit is returned to its initial condition.

(6) With a sign test positive and the bias negative, a signal appears onconductor 42 to reverse the polarity of the bias signal.

(7) With a sign test negative and the bias positive, a signal appears onconductor 42 to reverse the polarity of the bias signal.

(8) With a sign test negative and the bias negative, a command issupplied on conductor 45 to continue the comparison of the input signaland the stored signal.

The overall result of this operation is that no print commands will begenerated unless the peak height digitizer has first determined that theinput signal has actually begun to increase again and second, that thetop of another peak has been identified.

FIG. 4 illustrates an alternative form of apparatus for performing themethod of the present invention. Only the spectrum digitizer portion ofthe apparatus of FIG. 2 is illustrated in this figure; it should beunderstood that a mass number digitizer may be actuated by the printcommand signal derived from this apparatus. The mass spectrum signalsappear on conductor 61 and actuate a digital voltmeter 62 to provide anoutput digital signal on conductor 63 to a printer 64. The printerrequires a print command signal before it will record the input digitalsignals and the print command signal is supplied by the followingapparatus operative to identify a peak in the input signal.

The peak identifying apparatus of FIG. 4 comprises a comparator 65having an input mass spectrum signal on conductor 66, an input analogsignal (proportional to the stored digital signal) on conductor 67 fromthe voltmeter 62 and an input bias signal on conductor 68 from the biassource 69. The comparator supplies a signal on conductor 71 when theinput on conductor 66 is larger than the signal on conductor 67 plus thebias and a signal on conductor 72 when the input on conductor 66 issmaller than the signal on conductor 67 minus the bias. A signal onconductor 71 opens gate 73 allowing clock pulses from clock 75 to gothrough this gate; a signal on conductor 72 allows clock pulses to gothrough gate 74.

Taking first the operation of gate 73, when that gate is opened by asignal on conductor 71 indicating that the input mass spectrum signalhas become larger than the stored digital signal plus the bias, a signalwill be transmitted on conductor 76 to gate 77. Gate 77 is a normallyopen gate and will transmit the signal on through to conductor 78 tocause the digital voltmeter 62 to perform a new read function and tothus increase its stored quantity. Taking now gate 74, when a signalappears on conductor 72 indicating that the input mass spectrum signalhas become less than the stored digital signal minus the bias, a signalwill appear on conductor 79 to be supplied as a set signal on conductor81 to a flip-flop 82. The signal on conductor 79 will also be suppliedto a delay circuit 83 and, after an appropriate delay, will be suppliedthrough conductor 84 to gate 77. If gate 77 is then open, the signalwill be carried on conductor 78 to cause the voltmeter 62 to again makea new signal determination.

Actuation of the flip-flop 82 causes its circuit to perform twofunctions, First, it transmits a signal through gate 85 to a scondflip-flop 86, and second, it changes the condition of flip-flop 82 toblock further set signals until the flip-flop has been returned to itsoriginal condition. Flip-flop 86 performs the same two functions byfirst transmitting a print command to conductor 87 and by changing itscondition to block further signals until it has been returned to itsoriginal condition.

The print command on conductor 87 causes the printer 64 to record thesignal supplied to it on conductor 63. When the recording has beencompleted, a signal will be supplied on conductor 88 to reset flip-flop86. The print command signal on conductor 87 is also supplied to gate 77to cause that gate to block further signals to the digital voltmeter sothat the voltmeter cannot change its reading until the printer hascompleted its operation and the reset pulse has been supplied onconductor 88. The return of the flip-flop 86 to its original conditioncauses gate 77 to be returned to its open condition.

Gate 85 is controlled to establish a minimum signal level for actuationof the printer 64. To accomplish that purpose the input mass spectrumsignal appears on conductor 89 and is supplied to a comparator 91. Alsosupplied to the comparator is an offset level signal on conductor 92from offset source 93. If the signal on conductor 89 is greater than thesignal on conductor 92, the comparator 91 will supply an output signalon conductor 94 to open gate 85 and thus permit it to pass print commandsignals. If the input mass spectrum signals are lower than a prescribedlevel, gate 85 will be closed and no print commands will appear.

After a print operation has been initiated by a signal on conductor 79causing flip-flop 82 to be placed in its second condition, no furtherpeak signals can be supplied to the printer until the flip-flop has beenreset. A reset pulse is supplied on conductor 95 from gate 73 when thesignal on conductor 71 indicates that the input spectrum signal hasbegun to exceed the previously stored voltmeter signal by an amountlarger than the bias signal. When that condition exists the flip-flop 82will be returned to its first condition and peak identifying signals maybe passed to establish a print command signal on conductor 87.

While a certain preferred embodiment of the present invention has beenspecifically disclosed, it is to be understood that the invention is notlimited thereto, as many variations will be readily apparent to thoseskilled in the art and the invention is to be given its broadestpossible interpretation within the terms of the following claim:

What is claimed is:

1. Apparatus for identifying a peak amplitude value of signals within atime varying signal comprising in combination:

(a) means for sensing the instantaneous value of said time varyingsignal,

(b) means for storing sensed values of said time varying signal,

(c) means for selecting an initial value of said time varying signalabove a fixed amplitude value including means for energizing saidstoring means with said initial value,

(d) a source of bias signal and means for repeatedly reversing thepolarity of said bias signal,

(e) a summing means and means for energizing said summing means withsaid bias signal and said stored signal, said summing means includingmeans for producing an output signal constituting said stored signal andsaid repeatedly reversing bias signal, to produce alternately an addedsignal and a difference signal,

(f) a comparison means and circuit means for energizing said comparisonmeans with said sensed instantaneous value of said time varying signaland alternately said added signal and said difference signal, saidcomparison means including means for producing an output signalresulting from said comparison,

(g) a logic circuit including means for sensing sequentially thepolarity of said comparison means output signals and means for (1)energizing said storing means with the sensed instantaneous value ofsaid time varying signal when said comparison means output signal is ofone polarity when said output signal represents comparison of said addedsignal and said sensed instantaneous value of said time varying signal(2) and for withdrawing said stored value as a peak amplitude valuewithin said time varying signal when said comparison means output signalis of the opposite polarity when said output signal representscomparison of said difference signal and said sensed instantaneous valueof said time varying signal,

(h) and printing means actuated by said logic circuit upon sensing ofsaid output signal of said opposite polarity for withdrawing of saidstored value so as to produce a printed record of said withdrawn valueas said identified peak amplitude value of signals within said timevarying signal.

